The present invention relates to a semiconductor device used for an electrostatic microphone and others.
Multiple electret capacitor microphones (hereinafter called ECM) which can be easily miniaturized are used for a mobile telephone. Technique for configuring a capacitor on a semiconductor substrate where integrated circuits such as an amplifier are configured to realize the further miniaturization is disclosed in Japanese Patent Publication No. 11-88992 for example. To detailedly describe the technique, a stationary electrode layer is formed on a semiconductor substrate, a vibrating diaphragm is attached over the stationary electrode layer via a spacer and a capacitor is composed by the stationary electrode layer and the vibrating diaphragm.
FIG. 4 shows the structure. A stationary electrode layer 112, an insulating film 113, a spacer 114 and a vibrating diaphragm 115 are sequentially laminated on the surface of a silicon semiconductor substrate 111 and the lamination is installed in a package 118 having a hole 116. A reference number 117 denotes cloth and it is provided if necessary. A junction-type FET for impedance conversion, further an amplifier and a noise canceling circuit and others are integrated on the surface of the semiconductor substrate 111 according to a normal semiconductor process. The capacitance value of a capacitor formed by the vibrating diaphragm 115 and stationary electrode layer 112 varies because aerial vibration vibrates the vibrating diaphragm 115, the variation of the capacitance value is input to the FET and the FET converts it to an electric signal.
However, the capacitor microphone cannot be housed in a complete sealed container because of its property. Structure that aerial vibration can reach the vibrating diaphragm 115 via the hole 116 is necessarily required. The maintenance of a state in which aerial vibration is enabled means that it is also impossible to completely intercept light.
At least a few circuit elements integrated in the semiconductor substrate 111 are composed of PN junction. When light is incident on such a silicon semiconductor substrate having PN junction, dark current is caused by photoelectromotive force. There is a defect that the caused dark current flows in the circuit element, noise is caused and the malfunction of the circuit is caused.
The present invention is made to solve the problem described above.
According to first aspect of the invention, a semiconductor device comprising: a semiconductor substrate in which circuit elements are integrated; a stationary electrode layer formed over the semiconductor substrate; a spacer formed around the stationary electrode layer over the semiconductor substrate, for attaching a vibrating diaphragm composing a capacitor together with the stationary electrode layer; a dummy island provided in the semiconductor substrate surrounding the stationary electrode layer; and means for applying fixed potential to the dummy island.
According to the second aspect of the invention, a semiconductor device defined as the first aspect of the invention, further comprising a shield metal for intercepting light, wherein the circuit element arranged around the stationary electrode layer, wherein the shield metal is formed so that the circuit element is covered, wherein the dummy island is arranged between the shield metal and the stationary electrode layer.
According to the third aspect of the invention, a semiconductor device defined as the first aspect of the invention, wherein the fixed potential is supply potential Vcc.
According to the fourth aspect of the invention, a semiconductor device comprising: a semiconductor substrate includes a one conductive type of semiconductor layer, a reverse conductive type of epitaxial layer formed on the semiconductor layer, and plural islands formed to separate the epitaxial layer by one conductive type of separated areas; a circuit element formed in the island; a stationary electrode layer formed over the semiconductor substrate; a spacer formed around the stationary electrode layer over the semiconductor substrate, for attaching a vibrating diaphragm composing a capacitor together with the stationary electrode layer; a dummy island separated by the separated area, which is provided in the semiconductor substrate surrounding the stationary electrode layer; and means for applying fixed potential to the dummy island.
According to the fifth aspect of the invention, a semiconductor device defined as the fourth aspect of the invention further comprising shield metal for intercepting light formed over the island having the circuit element.
According to the sixth aspect of the invention, a semiconductor device defined as the fifth aspect of the invention, wherein the shield metal further covers a part of the dummy island.
According to the seventh aspect of the invention, a semiconductor device defined as the fifth aspect of the invention, wherein the shield metal is separated from the stationary electrode layer in a horizontal direction by a clearance portion.
According to the eighth aspect of the invention, a semiconductor device defined as the seventh aspect of the invention, wherein the clearance portion is arranged above a part of the dummy island.
According to the ninth aspect of the invention, a semiconductor device defined as the fourth aspect of the invention, wherein the fixed potential is supply potential Vcc.
According to the tenth aspect of the invention, a semiconductor device defined as the fourth aspect of the invention, wherein a ground potential GND is applied to the semiconductor layer and the separated areas.
According to the eleventh aspect of the invention, a semiconductor device defined as the fourth aspect of the invention, wherein PN junction formed by the dummy island composes a dummy photodiode.